memory performance issue

i am using c,c++ to develop a project and its a client server multi threaded application
when i run the server application it do some database transactions and sit idle if now
even no client is requesting i have seen memory used by app (shown in task manager )
is varying very much around 6000 k to 800 k and its automaticaly increases and decrease without any client request i m not getting why application behaving like this.

If it drops significantly then maybe Windows is swapping unused memory out to swapfile while other stuff needs it. If the application works fine and doesn't crash due to lack of memory then it's probably working find and not leaking memory.